If you get this error message while logging in to a Windows Vista computer using Terminal Services, here is the magic sauce.

http://blogs.msdn.com/spatdsg/archive/2007/03/14/atbroker-exe-application-error.aspx

I don't know anything about the problem to be honest, but the solution (Ctrl+Alt+End, log off, cancel log-off if there's any prompting) has worked for me, so I thought I'd pass the link along...